As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized sheet packaging material.
A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material. The packaging material has a multilayer structure comprising a layer of base material, e.g. paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material comprises a layer of oxygen-barrier material, e.g. aluminium foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material eventually forming the inner face of the package contacting the food product.
As is known, packages of this sort are produced on fully automatic packaging lines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized, e.g. by applying a chemical sterilizing agent such as a hydrogen peroxide solution, which is subsequently removed from the surfaces of the packaging material, e.g. evaporated by heating; and the web of packaging material so sterilized is maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.
Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).
In both the above cases, the finished packages are fed successively to a grouping unit, where they are formed into separate groups of a given number, which are eventually packed in packing material, e.g. cardboard or plastic film, to form respective packs for transport to retailers.
More specifically, the packages are fed to the grouping unit in lines parallel to the travelling direction, and are temporarily accumulated at a receiving station; a predetermined number of packages at the receiving station are then fed onto a conveyor for transfer to an output station. Along the path defined by the conveyor, the packages in each group are aligned into one or more lines crosswise to the travelling direction, and are then pushed to the output station, where they are packed in packing material to form a relative pack.
One example of a known grouping unit, suitable for grouping plastic bottles, is illustrated in U.S. Pat. No. 6,793,064.
More specifically, the above unit substantially comprises a continuous belt conveyor having a straight flat conveying branch, onto which the bottles are fed, at predetermined time intervals and in groups of a predetermined number, for transfer to a downstream packing station, where each group of bottles so formed in packed for delivery to retailers.
As they are fed to the packing station, the bottles in each group are first aligned into a specific configuration, and are then pushed, in that configuration, to the packing station. This is done by means of two separate mechanisms—an aligning mechanism and a push mechanism—arranged in succession in the travelling direction of the bottles.
The aligning mechanism is located over the conveyor, and comprises a number of aligning bars extending crosswise to the travelling direction of the bottles, and which are fed by a chain drive device along an endless path having a portion facing and parallel to the conveying branch of the conveyor.
Each group of bottles fed onto the conveyor comes to rest against a relative downstream aligning bar travelling slower than the conveyor.
The aligning bars therefore provide for slowing the bottles down slightly with respect to the speed of the conveyor, so as to compact the bottles in the travelling direction and align them into one or more lines crosswise to the travelling direction. The aligning bars also prevent the bottles from toppling over on the conveyor.
The push mechanism is located over the conveyor and downstream from the aligning mechanism in the travelling direction of the bottles, and, like the aligning mechanism, comprises a number of push bars extending crosswise to the travelling direction of the bottles, and which are fed by a further chain drive device along an endless path having a portion facing and parallel to the conveying branch of the conveyor.
Where the aligning bars release the relative groups of bottles, each push bar interacts with the upstream side of the bottles in each group to push the group to the packing station at the same speed as the conveyor.
Known units of the type described above are extremely bulky, leave room for improvement as regards output, and are subject to relatively severe acceleration and deceleration forces resulting in possible slippage between the packages and the conveyor.